Typically, the machines and equipment used at many production sites are controlled by a control device such as a programmable controller (also referred to below as a Programmable Logic Controller, PLC).
Communications between the PLC and one or multiple remote IO terminals may be implemented using polling, and in this case, the PLC acts as a master device managing all communications. For example, Japanese Unexamined Patent Publication No. 2007-312043 discloses a communication protocol where communications between the master device and slave device in a remote IO system typically use either broadcast or polling.